1. Technical Field
The present disclosure relates to controlling a switching power converter to reduce distortion of the output voltage waveform of the power converter when transitioning to low-load or no-load conditions.
2. Description of the Related Arts
The efficiency demands placed on portable electronic devices create challenges for regulating power under changing load conditions. These challenges include consuming nearly no power in standby mode, while delivering full power when the device is suddenly plugged-in for active power mode operation. And for many battery operated devices, these demands for power savings increasingly focus on low-load and no-load energy savings.
To address these challenges many portable electronic devices use switching power regulators that operate in different operating modes based on load conditions. For example, a switching power converter typically uses PWM (pulse width modulation) during heavy load conditions and PFM (pulse frequency modulation) during light load conditions. PWM operation mode is generally more efficient than PFM operation mode at higher load conditions where dynamic losses, including conduction losses and switching losses, dominate. On the other hand, PFM operation mode is generally more efficient than PWM operation mode at lower load conditions where static losses such as quiescent current drawn by the switching power converter dominate. Using these techniques, multi-mode switching power converters offer improved efficiency over a wider range of load conditions.
But, using multi-mode operation may introduce distortions in the output voltage caused by switching from one mode to another. These distortions may result from discontinuity in the regulation of the switching power converter at the transition point between different operating modes. Discontinuities may arise, for example, when the control voltage requirements from the two operating modes differ at the transition point. These differences may create an undesired amount of output voltage ripple at the transition point. Further, without knowledge of transformer characteristics of the switching power converter, it may even be difficult to predetermine the transition point depending on the operating mode used to regulate the power on either side of the transition point (i.e., boundary).